#include<stdio.h>
#include<math.h>
int main()
{   	   	 		 
    float a, b, c;
    float s, area;

    printf("Input a,b,c:");
    scanf("%f,%f,%f", &a, &b, &c);               //1

    if (a + b > c && a + c > b && b + c > a)     //2
    {   	   	 		 
        s = (a + b + c) / 2;                     //1  
        area = sqrt(s * (s - a) * (s - b) * (s - c));//1
        printf("area=%.2f", area);
    }
    else                                         //2
        printf("Input error!");

    return 0;
}